When we're forwarding syslog messages to a remote host we can get temporary
failures such as EAGAIN or ECONNREFUSED from the sendmsg() call. These are not
fatal. Future attempts to send might succeed. Don't mark the remote target as
F_UNUSED so we'll try to log again on future messages.

While here remove the commented out ENOBUFS case, because we actually handle
that (by ignoring it, so we retry with future logs).

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